Spinal fusion surgery for degenerative disc disease involves removing the damaged disc and replacing it with bone grafted from another site on the patient's body, bone from a donor, or artificial or synthetic bone graft material that stimulates bone growth to fuse, or join, the two vertebrae together to stabilize the spine. In all spinal interbody fusion surgeries, disc material is removed. A spacer, referred to as a “cage” is then inserted into the disc space. It is critical that the cage placed in the space formerly occupied by the disc has effective contact with the endplates of the vertebrae in order for the surgery to promote the fusion of the vertebrae and to avoid fracture of the endplates.
There are many versions of bone cages known in the art, and many attempts have been made to solve the problem of stable placement of bone cages with the optimum and controlled contact with the vertebral endplates. However, devices known in the art are associated with problems due to incomplete or uncontrolled contact between the endplates of the vertebral bodies and the upper and lower surfaces of the cage. Many attempts have been made in the art to create a bone cage which can be adjusted or positioned to account for physiological differences in patients and achieve pressure reduction.
Expandable bone cages are known in the art. An expandable bone cage may be expanded after it is inserted, allowing the surgeon to adjust the height of the bone cage to fit each specific patient. One example of an expandable bone cage is the VBoss Implant by Stryker. The VBoss Implant has an expandable column with modular end caps that are available in 5 diameters with 0, 5, or 10 degree angles to enhance restoration of lordsis. The XPand® by Globus Medical is an expandable cage that comes in a variety of footprints, heights, and lordotic angles. Both of these devices can be expanded vertically; however, these cages are indicated in cases to replace the whole vertebra body after the entire vertebral bone is removed.
U.S. Pat. No. 6,852,129 (Gerbec '129) teaches a wedge-shaped bone fusion implant with expandable sidewalls that allows the height of the implant to be adjusted when a component is inserted for expansion. This design requires that the physician manually control expansion and determine the position of the plates of the device without mechanical guidance or physical precision. In addition, the flattened and rectangular plates of the device do not accomplish effective contact with the endplates, and this leaves a gap between the surfaces of the device and the endplates.
U.S. Pat. No. 6,962,606 (Michelson '606) teaches an adjustable “push in” implant by which the “front, back or both” of the implants are raised by “the same or various amounts.” The implant taught by Michelson '606 is expandable; however, placement of the Michelson '606 device requires a rectangular “blocker” component to keep the ends apart and the expansion is not effectively controlled. The lack of controlled expansion of the device may result in substantial risk to a patient because the bone cage may pack or break through the bone of the vertebral bodies if expanded too far. In addition, this device has only two positions: open and closed.
It is desirable to have a component for a bone cage which allows the bone cage to be expanded with maximum control and predictability of expansion.
It is desirable to have a reliable means for expanding a bone cage device.